Eric Siebert at Techtarget has a write up on Snaps ( part 2 ) titled Deleting virtual machine snapshots without wasting disk space
Taking snapshots of your virtual machines is a useful way to preserve and restore ESX configurations; however, proper management is needed to avoid performance problems. In this tip, we’ll explore advanced snapshot management topics. (For snapshot basics or to review how snapshots work, see my previous tip.)
Eric does a great job of explaining the disk space used when deleting a snapshot, and performance factors.